Technical Field
[0001] The present invention relates to wireless communication, and more specifically, to
a method for allocating pilots to reduce channel estimation errors in a wireless communication
system.
Background Art
[0002] Third generation partnership project (3GPP) mobile communication systems based on
a wideband code division multiple access (WCDMA) radio access technique are widely
spread all over the world. High speed downlink packet access (HSDPA) that can be defined
as a first evolutionary stage of WCDMA provides 3GPP with a wireless access technique
that is highly competitive in the mid-term future. However, since requirements and
expectations of users and service providers are continuously increased and developments
of competing radio access techniques are continuously in progress, new technical evolutions
in 3GPP are required to secure competitiveness in the future.
[0003] One of the systems being taken into consideration after the third generation is an
orthogonal frequency division multiplexing (OFDM) system that can reduce the intersymbol
interference effect with low complexity. The OFDM transforms serially inputted data
symbols into N parallel data symbols and transmits the parallel data symbols with
loaded on N sub-carriers separated from each other. The sub-carriers maintain orthogonality
in terms of frequency. Each of orthogonal channels experiences mutually independent
frequency selective fading, and the spaces between transmitted symbols become wider,
and thus interference between the symbols can be minimized. Orthogonal frequency division
multiple access (OFDMA) is a multiple access method that realizes a multiple-access
by independently providing some of available sub-carriers to each user in a system
that uses OFDM as a modulation method. The OFDMA provides frequency resources, which
are referred to as sub-carriers, to each user, and each of the frequency resources
are independently provided to a plurality of users, and thus the frequency resources
are generally not overlapped with each other. As a result, the frequency resources
are mutual-exclusively allocated to each user.
[0004] One of the major problems of the OFDM/OFDMA is that peak amplitude of a transmission
signal can be considerably higher than average amplitude. This peak-to-average power
ratio (PAPR) problem is originated from the fact that an OFDM signal is the sum of
N sinusoidal signals on sub-carriers different from each other. In order to save transmission
power, it is needed to lower the PAPR.
[0005] One of the systems proposed to lower the PAPR is single carrier - frequency division
multiple access (SC-FDMA). SC-FDMA is a type that combines frequency division multiple
access (FDMA) with existing single carrier - frequency division equalization (SC-FDE)
method. The SC-FDMA has a characteristic similar to that of the OFDMA in that signals
are modulated and demodulated in a time domain and a frequency domain using discrete
Fourier transform (DFT), but it is advantageous in saving transmission power since
the PAPR of a transmission signal is low. Particularly, in connection with usage of
a battery, it is advantageous for an uplink that connects a user equipment sensitive
to transmission power to a base station.
[0006] The 3GPP Draft No. R1-062562, entitled "Uplink reference signal multiplexing method",
describes reference signal transmission methods in Evolved UTRA uplink.
[0007] In order to efficiently restore data at a receiver, channel information should be
obtained. The channel information is used for modulating and demodulating the data
or scheduling users. Generally, the channel information is obtained based on a pilot
contained in a signal transmitted by a transmitter. However, an efficient pilot structure
has been not widely known yet.
Disclosure of Invention
Technical Problem
[0008] An object of the invention is to provide a method for allocating pilots to increase
system capacity.
Technical Solution
[0009] In one aspect, there is provided a method for allocating pilots to a sub-frame as
set forth in the appended claims.
[0010] In another aspect, there is provided a user equipment for allocating pilots to a
sub-frame as set forth in the appended claims.
Advantageous Effects
[0011] System capacity can be increased, and degradation of performance incurred by a channel
estimation error can be minimized.
Brief Description of the Drawings
[0012]
FIG. 1 is an exemplary view showing a mobile communication system.
FIG. 2 is a block diagram showing a transmitter according to an embodiment of the
present invention.
FIG. 3 is an exemplary view showing a sub-frame transmitted by the transmitter.
FIG. 4 is an exemplary view showing a signal structure of a CDM method.
FIG. 5 is an exemplary view showing a signal structure of an FDM-L scheme.
FIG. 6 is an exemplary view showing a signal structure of an FDM-D scheme.
FIG. 7 is an exemplary view showing a sub-frame structure when TTI=1ms.
FIG. 8 is an exemplary view showing pilot allocation according to an embodiment of
the present invention.
FIG. 9 is an exemplary view showing pilot allocation according to another embodiment
of the present invention.
FIG. 10 is an exemplary view showing pilot allocation according to still another embodiment
of the present invention.
FIG. 11 is an exemplary view showing pilot allocation according to still another embodiment
of the present invention.
FIG. 12 is an exemplary view showing pilot allocation according to still another embodiment
of the present invention.
FIGs. 13 to 18 are exemplary views showing pilot allocation according to still another
embodiment of the present invention.
FIG. 19 is an exemplary view showing pilot allocation according to still another embodiment
of the present invention.
FIGs. 20 to 25 are exemplary views showing pilot allocation according to still another
embodiment of the present invention.
FIG. 26 is an exemplary view showing pilot allocation according to still another embodiment
of the present invention.
FIG. 27 is an exemplary view showing pilot allocation according to still another embodiment
of the present invention.
FIG. 28 is an exemplary view showing pilot allocation according to still another embodiment
of the present invention.
Mode for the Invention
[0013] FIG. 1 is an exemplary view showing a mobile communication system.
[0014] Referring to FIG. 1, a mobile communication system comprises a base station and a
plurality of user equipments (UEs). This can be a single carrier - frequency division
multiple access (SC-FDMA) system. The mobile communication system is widely deployed
to provide a variety of communication services such as voices, packet data, or the
like.
[0015] The base station 10 generally is a fixed station that communicates with the user
equipment 20 and can be referred to as another terminology, such as a node-B, base
transceiver system (BTS), access point, or the like.
[0016] A user equipment 20 can be fixed or mobile and can be referred to as another terminology,
such as a mobile station (MS), user terminal (UT), subscriber station (SS), wireless
device, or the like.
[0017] Hereinafter, downlink means a communication from the base station 10 to the user
equipment 20, and uplink means a communication from the user equipment 20 and the
base station 10. In the downlink, a transmitter can be a part of the base station
10, and a receiver can be a part of the user equipment 20. In the uplink, a transmitter
can be a part of the user equipment 20, and a receiver can be a part of the base station
10. The base station 10 can include a plurality of receivers and transmitters, and
the user equipment 20 can include a plurality of receivers and transmitters.
[0018] FIG. 2 is a block diagram showing a transmitter according to an embodiment of the
present invention.
[0019] Referring to FIG. 2, the transmitter 100 incldues a discrete Fourier transform (DFT)
unit 110, a sub-carrier mapper 120, an inverse fast Fourier transform (IFFT) unit
130, and a cyclic prefix (CP) insert unit 140.
[0020] The DFT unit 110 performs DFT on an input signal s and transforms the input signal
into frequency domain signals x. If it is assumed that Nb is the number of sub-carriers
for a certain user, the operation of the DFT unit 110 can be expressed as shown
where F
Nb×Nb is a DFT matrix having a size of Nb used for spreading data symbols.
[0021] The sub-carrier mapper 120 performs sub-carrier mapping on spreaded frequency domain
signals x in a certain sub-carrier allocation method. The IFFT unit 130 performs IFFT
on signals x' allocated by the sub-carrier mapper 120 and converts the signals into
a time domain signal y. The time domain signal y can be said as an OFDM symbol, which
can be expressed as shown
[0022] The sub-carrier mapper 120 performs sub-carrier mapping on spreaded frequency domain
signals x in a certain sub-carrier allocation method. The IFFT unit 130 performs IFFT
on signals x' allocated by the sub-carrier mapper 120 and converts the signals into
a time domain signal y. The time domain signal y can be said as an OFDM symbol, which
can be expressed as shown
where F
-1N×N is an IFFT matrix having a size of N, which is used for transforming a frequency
domain signal into a time domain signal.
[0023] The CP insert unit 140 inserts a CP into the time domain signal y, and the CP-inserted
signal is converted into an analog signal by the RF unit 150 and propagated into a
radio channel through an antenna 160. The method of generating a transmission signal
and transmitting the transmission signal to the receiver by the transmitter is referred
to as SC-FDMA. The size of the DFT or IFFT matrix can be varied.
[0024] FIG. 3 is an exemplary view showing a sub-frame transmitted by the transmitter. The
length of the sub-frame can be called as a transmission time interval (TTI). Here,
the TTI is 0.5 millisecond (ms), but not limited to.
[0025] Referring to FIG. 3, a sub-frame contains six long blocks (LB) and two short blocks
(SB). The long block LB is a block having a time interval longer than that of the
short block SB. Neither the long block LB nor the short block SB has an absolute size.
The short block SB includes a first short block SB#1 and a second short block SB#2.
Here, the first short block SB#1 precedes the second short block SB#2 in the aspect
of time. That is, the first short block SB#1 is transmitted prior to the second short
block SB#2.
[0026] Although the long block LB is used for control and/or data transmission, it also
can be used for transmitting a reference signal. The reference signal is also called
as a pilot. If the pilot is contained in the long block LB, the long block LB can
be referred to as a pilot block. The short block SB can be used for control and/or
data transmission or can be used for transmitting a pilot. If the pilot is contained
in the short block SB, the short block SB can be referred to as a pilot block. A cyclic
prefix (CP) is inserted in each of the long block LB and the short block SB to minimize
interference between symbols and interference occurred by multiple path channel.
[0027] The time interval of the short block SB can be shorter than the time interval of
the long block LB. The time interval of the short block SB is not limited, but it
can be preferably 0.5 times of the time interval of the long block LB. Due to duality
of the time domain and frequency domain, the frequency band of the short block SB
is twice as wide as the frequency band of the long block LB if the time interval of
the short block SB is 0.5 times of the time interval of the long block LB. In addition,
the number of sub-carriers of the long block LB is twice as many as the number of
sub-carriers of the short block SB. In order to clarify the explanation, hereinafter,
it is assumed that the time interval of the short block SB is 0.5 times of the time
interval of the long block LB.
[0028] Although the time interval of the first short block SB#1 is the same as the time
interval of the second short block SB#2, it is not a limitation, but they can have
time intervals different from each other. In addition, the time interval of the short
block SB can be dynamically modified depending on the time interval of the long block
LB or a situation of a system.
[0029] A sub-frame contains six long blocks LB and two short blocks SB, but the number of
the long blocks and the short blocks contain in the sub-frame is not limited. The
sub-frame may contain at least one long block and at least one short block.
[0030] Although four long blocks LB are arranged between two short blocks SB in the sub-frame,
the arrangement of the short blocks SB and the long blocks is not limited, but can
be diversely modified depending on a system. For example, three long blocks LB can
be arranged between short blocks SB, or five long blocks LB can be arranged. In addition,
arrangement of the short blocks SB can be dynamically modified within the sub-frame
depending on performance or environment of a system.
[0031] A pilot is data previously known between the transmitter and the receiver and can
be classified into two types depending on its usage. One is a channel quality (CQ)
pilot for measuring channel quality in order to schedule users and to apply an adaptive
modulation and coding (AMC) scheme. The other is a data demodulation (DM) pilot for
estimating a channel in order to demodulate data. The CQ pilot is transmitted at a
predetermined time in the frequency domain, and the base station grasps the channel
state of the user equipment using this information and schedules user equipments in
a predetermined scheduling method. Accordingly, for uplink scheduling of the base
station, creating a large number of orthogonal channels within a limited time and
frequency domain so that a large number of user equipments within a cell may transmit
CQ pilots will affect capacity of the system. On the other hand, the DM pilot is a
pilot that is transmitted within the time and frequency domain when the user equipment
is scheduled and transmits data in the time and frequency domain.
[0032] A pilot can be categorized into a CQ pilot and a DM pilot by usage. It is general
that the pilot is the DM pilot if the pilot is transmitted within the frequency band
of a corresponding user equipment, whereas the pilot is the CQ pilot if the pilot
is transmitted throughout a frequency band scheduled wider than the frequency band
of the user equipment by the base station. Accordingly, when the pilot is used as
the CQ pilot, it can also be used as the DM pilot.
[0033] Since there are a plurality of user equipments in a base station or in a sector,
each user equipment needs to be discriminated. Particularly, a pilot block should
be distinguished between user equipments by using orthogonality.
[0034] The orthogonality is divided into a time domain orthogonality, a frequency domain
orthogonality, and a code domain orthogonality. The time domain orthogonality has
a problem in that an accurate transmission timing control is needed. Accordingly,
in an SC-FDNA system, the frequency domain orthogonality or the code domain orthogonality
has a further superior characteristic.
[0035] The frequency domain orthogonality can be accomplished by transmitting a signal of
each of user equipment through a different sub-carrier. Hereinafter, a signal structure
using a signal orthogonal in the frequency domain is referred to as frequency division
multiplexing (FDM). In the FDM, frequency bands of respective user equipments allocated
to a sub-carrier are not overlapped with each other. The frequency domain orthogonality
can be applied to a localized signal structure or a distributed signal structure.
A localized signal occupies continuous spectrums, and a distributed signal occupies
comb-shaped spectrums. Hereinafter, a signal structure using the localized signal
is referred to as frequency division multiplexing ? localized (FDM-L), and a signal
structure using the distributed signal is referred to as frequency division multiplexing
? distributed (FDM-D).
[0036] The code domain orthogonality is accomplished by transmitting a signal of each user
equipment through a common sub-carrier. The entire or a portion of a frequency band
allocated to a sub-carrier for each user equipment is overlapped. Hereinafter, a signal
structure using a signal orthogonal in the code domain is referred to as code division
multiplexing (CDM).
[0037] FIG. 4 is an exemplary view showing a signal structure of a CDM method.
[0038] Referring to FIG. 4, sub-carriers of a pilot signal are transmitted in an overlapped
manner for M users (user equipments). The pilot is loaded on the short block SB, and
the CDM performs multiplexing among user equipments through the code orthogonality
by allocating a code sequence to the entire bands of the short block SB.
[0039] Sub-carriers of the short block SB can be allocated throughout the overall frequency
band. Here, the overall frequency band is a frequency band including all frequency
bands of the user equipments scheduled within a base station or a sector. The short
block SB is in the form of overlapped frequency bands of user equipments. The short
block SB maintains orthogonality of each user equipment in the code domain.
[0040] A constant amplitude zero auto-correlation (CAZAC) sequence can be used as a code
sequence. Generally, there are two types of CAZAC sequences, a GCL CAZAC and a Zadoff-Chu
CAZAC. The two types of sequences are in a conjugate relation. For example, the Zadoff-Chu
CAZAC can be obtained by applying a conjugate to the GCL CAZAC.
[0041] In the Zadoff-Chu CAZAC, the k-th entry CAZAC sequence can be expressed as shown
where M denotes a root index and N denotes the length of a CAZAC sequence. M is a
prime relative to N.
[0043] Equation 4 means that the size of the CAZAC sequence is always one. Equation 5 means
that auto correlation of the CAZAC sequence is expressed as a Dirac-delta function.
The auto correlation is based on circular correlation. Equation 6 means that the cross
correlation is always a constant.
[0044] A pilot signal loaded on the short block SB can be used as a DM pilot for demodulating
a data signal transmitted on a sub-carrier of a long block of the same band. In addition,
since this pilot signal is transmitted throughout the overall frequency band, it can
be used as a CQ pilot for measuring channel quality.
[0045] FIG. 5 is an exemplary view showing a signal structure of an FDM-L scheme.
[0046] Referring to FIG. 5, sub-carriers are locally concentrated for M users (user equipments).
Different user equipments are allocated to different frequency bands, and frequency
division multiplexing is used.
[0047] Sub-carriers are locally concentrated in the short block SB and the long block LB
for each user equipment. A pilot is loaded on the sub-carrier of the short block SB.
If the time interval of the short block SB is 0.5 times of the time interval of the
long block LB, the sub-carrier of the short block SB occupies a band twice as wide
as that of the sub-carrier of the long block LB. Accordingly, two contiguous sub-carriers
of the long block LB make a pair with one sub-carrier of the short block SB.
[0048] In the FDM-L scheme, a pilot signal loaded on the short block SB can be used as a
DM pilot for demodulating a data signal transmitted on the sub-carrier of the long
block LB of the same band. It is since that the frequency band of the sub-carrier
of the short block SB is overlapped with that of the sub-carrier of the long block
LB. However, since the pilot signal is locally concentrated in the frequency domain
for a corresponding user equipment, it is difficult to be used as a CQ pilot for measuring
channel quality of the overall frequency band.
[0049] FIG. 6 is an exemplary view showing a signal structure of an FDM-D scheme.
[0050] Referring to FIG. 6, sub-carriers are distributed and non-contiguous for M users
(user equipments). Sub-carriers of the long block LB and the short block SB are allocated
to be distributed at regular intervals so that sub-carriers of the same user equipment
are not to be contiguous. That is, sub-carriers of a user equipment are distributed
at regular intervals.
[0051] Pilot signals allocated to the first short block SB#1 and the second short block
SB#2 are allocated in the frequency domain to be staggered from each other for respective
user equipments. If the time interval of the short block SB is 0.5 times of the time
interval of the long block LB, the sub-carrier of the short block SB occupies a band
twice as wide as the band of the a sub-carrier of the long block LB. Since two frequency
bands of the long block LB are arranged in one frequency band of the short block SB,
in the FDM-D scheme, pilot signals of two short blocks SB are alternatively allocated
for each user equipment with respect to the location of a sub-carrier of a user equipment
corresponding to the long block LB. For example, a pilot signal for a first user equipment
302 of the long block LB is loaded on the sub-carrier 301 of the first short block
SB#1. A pilot signal for a second user equipment 303 of the long block LB in the same
band is loaded on the sub-carrier 304 of the second short block SB#2. Thereafter,
pilot signals are loaded on the sub-carriers of the short block SB for respective
user equipments of the long block LB in a subsequently staggered form.
[0052] In the FDM-D scheme, a pilot signal loaded on the short block SB can be used as a
DM pilot for demodulating a data signal transmitted on the sub-carrier of the long
block LB of the same band. It is since that the frequency band of the sub-carrier
of the short band SB is overlapped with the frequency band of the sub-carrier of the
long block LB. In addition, since this pilot signal is transmitted throughout the
overall frequency band, it can be used as a CQ pilot for measuring channel quality.
[0053] In the FDM-D scheme, only a pilot signal of either the first short block SB#1 or
the second short block SB#2 can be used at the location of a sub-carrier to which
data of the long block LB is allocated. Therefore, an interpolation cannot be performed
on the axis of time, and degradation of performance is invited in a time selective
channel environment in which moving speed of a user equipment is high.
[0054] When a 0.5 ms TTI is assumed, one sub-frame becomes one TTI. However, if the TTI
is expanded to 1 ms, it becomes a different matter.
[0055] FIG. 7 is an exemplary view showing a sub-frame structure when TTI=1ms.
[0056] Referring to FIG. 7, it is a form of repeating the sub-frame of FIG. 3 under the
assumption that the same sub-frame is maintained. There are 12 long blocks LB for
transmitting data and 4 short blocks SB for transmitting pilots.
[0057] One of the problems of the sub-frame structure is that although CQ pilots are allocated
to all resources, i.e., all sub-carriers, corresponding to the short block SB, the
number of user equipments that can be multiplexed is limited. That is, since the number
of sub-carriers allocated to one short block SB is only a half of the number of sub-carriers
allocated to one long block LB, the length of a CAZAC sequence is short, and thus
the number of cases where circulation is delayed is limited. Furthermore, if DM pilots
and CQ pilots are multiplexed within the same short block SB in the FDM scheme, intervals
of sub-carriers of the CQ pilot are increased, and thus the number of CAZAC sequences
is decreased, which makes cell planning difficult as a result. Due to distribution
of power for DM pilots and CQ pilots and decrease of the intervals of sub-carriers
on the frequency domain, performance of channel estimation also can be degraded.
[0058] In addition, as an example, three short blocks SB out of four short blocks SB can
be used as a DM pilot for demodulating data, and the other one short block SB can
be used as a CQ pilot for scheduling the frequency domain. At this point, since only
one short block SB is used as a CQ pilot, time spacing between short blocks SB that
exist between two sub-frames is not uniform, and thus efficiency of channel estimation
can be dropped. Furthermore, if CQ pilots are multiplexed among user equipments in
the CDM scheme, the number of user equipments that can be multiplexed is limited by
a CAZAC sequence.
[0059] Hereinafter, a method of allocating pilots according to the present invention will
be described.
[0060] FIG. 8 is an exemplary view showing pilot allocation according to an embodiment of
the present invention.
[0061] Referring to FIG. 8, the sub-frame contains 13 long blocks LB and 2 short blocks
SB. Comparing with the sub-frame of FIG. 7, two short blocks SB are modified to one
long block LB.
[0062] The two short blocks SB can be used as a DM pilot, and the one long block LB#7 can
be used as a CQ pilot. That is, sub-carriers are allocated to the short blocks SB
throughout the frequency band of a specific user equipment, and sub-carriers are allocated
to the long block LB#7 throughout a frequency band containing the frequency band of
a specific user equipment.
[0063] Although a long block LB#7 at the center is selected as a long block LB used as a
pilot block, a long block LB at another position can be selected. The two short blocks
SB can be arranged at positions respectively apart from the long block LB#7, which
is used as a pilot block, in the opposite directions. In this case, time spacing between
pilots is maintained, and thus efficiency of channel estimation can be enhanced. For
example, the two short blocks SB are respectively arranged five long blocks away from
the long block LB#7 in the opposite directions. The space between the long block LB#7,
i.e., a pilot block, and the short block can be appropriately modified depending on
situations.
[0064] The short blocks SB can build orthogonality among user equipments in FDM or CDM.
The long block LB#7 can build orthogonality among user equipments in CDM. A CAZAV
sequence can be used in the short blocks SB and the long block LB#7. At this point,
the short blocks SB can build orthogonality among user equipments within a cell in
FDM, and can build orthogonality among user equipments in different cells in CDM.
[0065] If a user equipment is identified in the CDM scheme since the long block LB#7 twice
as wide as the short block SB is used as a CQ pilot, the base station can multiplex
twice as many user equipments. It is since that the number of codes of a CAZAC sequence
depends on the length of the sequence. Furthermore, it is advantageous in allocating
sequences between adjacent cells. In addition, as the length of the sequence becomes
longer due to the characteristic of the CAZAC sequence, a cross correlation value
becomes smaller, and thus a processing gain also can be obtained accordingly.
[0066] The long blocks LB#7 used as a CQ pilot also can be multiplexed among a plurality
of user equipments in the CDM or FDM scheme. Since channel quality is measured throughout
the overall frequency band, it is possible to know a channel estimation value for
a data transmission band used for the long block LB (excluding the long block LB#7
used as a pilot block) to which a sub-carrier transmitted in a localized form is allocated.
Accordingly, a pilot contained in the long block LB#7 also can be used as a DM pilot
for demodulation.
[0067] In the method described above, since two short blocks SB are converted into one long
block LB, a length corresponding to one CP allocated to the long block LB remains,
and thus the length of the CP needs to be readjusted. In an embodiment, the length
of the one remaining CP can be uniformly allocated to all CPs within a 1 ms TTI. Therefore,
a delay spread of a channel that is larger than that of an existing structure can
be covered. In another embodiment, the one remaining CP is allocated to a pilot block.
For example, the CP is allocated to the long block LB#7 or a short block SB to which
a CQ pilot is allocated. Therefore, a further larger margin is put in a pilot block
to which a pilot is allocated, and thus deviated timing can be further easily updated.
[0068] FIG. 9 is an exemplary view showing pilot allocation according to another embodiment
of the present invention.
[0069] Referring to FIG. 9, in comparison with the sub-frame of FIG. 8, short blocks SB
are arranged at both ends. Two short blocks SB are respectively arranged six long
blocks away from the long block LB#7 in the opposite directions. The short blocks
SB can be used as a DM pilot, and the one ling block LB#7 can be used as a CQ pilot.
[0070] FIG. 10 is an exemplary view showing pilot allocation according to still another
embodiment of the present invention.
[0071] Referring to FIG. 10, two short blocks SB and two long blocks LB#6 and LB#12 are
used as a pilot within a 1 ms TTI. The short blocks are used as a DM pilot. The long
blocks LB#6 and LB#12 are used as a CQ pilot. In addition, since the long blocks LB#6
and LB#12 contain the frequency band of a specific user equipment, they also can be
used as a DM pilot, as well as a CQ pilot.
[0072] If the long blocks LB#6 and LB#12 twice as wide as the short blocks SB are used as
a pilot, and thus user equipments are multiplexed for CQ pilots in the CDM scheme,
system capacity can be increased compared with using the short blocks SB. In addition,
since two long blocks LB#6 and LB#12 are used as a pilot, accuracy of CQ measurement
and/or channel estimation can be enhanced.
[0073] FIG. 11 is an exemplary view showing pilot allocation according to still another
embodiment of the present invention.
[0074] Referring to FIG. 11, the positions of long blocks LB#5 and LB#11 on which pilots
are loaded are modified from the sub-frame of FIG. 10. The arrangement of two short
blocks SB and two long blocks LB#5 and LB#11 is not limited as shown in the figure,
but can be diversely modified.
[0075] FIG. 12 is an exemplary view showing pilot allocation according to still another
embodiment of the present invention.
[0076] Referring to FIG. 12, the long block LB#13 positioned at the end of the sub-frame
is used as a CQ pilot, and two short blocks SB and one long block LB#5 are used as
a DM pilot. This is a case where the long block LB#13 positioned at the end of the
sub-frame is used throughout the entire bands. If the CDM scheme is used to identify
a user equipment, the long block LB#13 can estimate channels of entire bands, and
thus it can be used as a DM pilot, as well as a CQ pilot. Even when the FDM scheme
is used to identify a user equipment, the long block LB#13 can estimate channels of
entire bands, and thus it can be used as a DM pilot, as well as a CQ pilot.
[0077] FIGs. 13 to 18 are exemplary views showing pilot allocation according to still another
embodiment of the present invention.
[0078] Referring to FIGs. 13 to 18, the long block LB#13 positioned at the end of the sub-frame
is used as a CQ pilot, and two short blocks SB and one long block LB#5 are used as
a DM pilot. FIGS. 13 to 18 shows sub-frames in which positions of the short blocks
and the long block used as a DM pilot are modified. Pilots are allocated while maintaining
the time space between the short blocks SB and the long block on which the pilots
are loaded so that channel estimation performance can be maintained in accordance
with changes in time.
[0079] The two short blocks SB and one long block on which DM pilots are loaded are not
limited to the forms shown in the figures, but can be diversely modified.
[0080] Hereinafter, a method of allocating pilots to a sub-frame configures only with long
blocks. That is, one sub-frame is configured with a plurality of blocks having a uniform
length.
[0081] FIG. 19 is an exemplary view showing pilot allocation according to still another
embodiment of the present invention.
[0082] Referring to FIG. 19, pilots are loaded on two long blocks LB#4 and LB#11, and at
least one of the long blocks is used as a CQ pilot. For example, a fourth long block
LB#4 is used as a DM pilot, and an eleventh long block LB#11 is used as a CQ pilot.
Alternatively, the fourth long block LB#4 is used as a CQ pilot, and the eleventh
long block LB#11 is used as a DM pilot. Both of the two long blocks LB#4 and LB#11
can be used as a CQ pilot. It is since that a CQ pilot also can be used as a DM pilot.
[0083] The two long blocks LB#4 and LB#11 can be used as a DM pilot, and one of the other
long blocks can be used as a CQ pilot. For example, the fourth long block LB#4 and
the eleventh long block LB#11 can be used as a DM pilot, and a first long block LB#1
can be used as a CQ pilot. Alternatively, the fourth long block LB#4 and the eleventh
long block LB#11 can be used as a DM pilot, and a fourteenth long block LB#14 can
be used as a CQ pilot. At this point, the interval of CQ pilots is equal to or longer
than the interval of DM pilots. For example, CQ pilots can be allocated to long blocks
at intervals of 1 TTI or longer than 1 TTI.
[0084] If only long blocks LB#4 and LB#11 are used as pilot blocks, and the CDM scheme is
used, the number of codes of a CAZAC sequence can be increased, and thus system capacity
is increased. In addition, the number of long blocks is increased by converting two
short blocks into one long block, and thus a data rate can be increased.
[0085] FIGs. 20 to 25 are exemplary views showing pilot allocation according to still another
embodiment of the present invention.
[0086] Referring to FIGs. 20 to 25, various arrangements of two long blocks on which pilots
are loaded are shown. Pilots are allocated while maintaining the time space between
long blocks on which the pilots are loaded so that channel estimation performance
can be maintained in accordance with changes in time.
[0087] The long blocks on which pilots are loaded are not limited to the forms shown in
the figures, but can be diversely modified. In addition, the number of long blocks
on which pilots are loaded is not limited to two, but pilots can be loaded on one
or more long blocks.
[0088] FIG. 26 is an exemplary view showing pilot allocation according to still another
embodiment of the present invention.
[0089] Referring to FIG. 26, pilots are loaded on two long blocks LB#1 and LB#13 and two
short blocks SB#1 and SB#2. Pilots are loaded on the long blocks LB#1 and LB#13 positioned
at both ends of 1 ms TTI.
[0090] The pilots of the long blocks LB#1 and LB#13 can be used as a DM pilot, and since
pilots of the short blocks SB#1 and SB#2 are allocated within a scheduling bandwidth
containing the frequency band of a specific user equipment or for the entire bands,
they can be used both as a CQ pilot and as a DM pilot. Since the long blocks LB#1
and LB#13 twice as wide as the short blocks SB#1 and SB#2 are used as a DM pilot,
accuracy of channel estimation can be enhanced on the axis of frequency.
[0091] FIG. 27 is an exemplary view showing pilot allocation according to still another
embodiment of the present invention.
[0092] Referring to FIG. 27, pilots are loaded on two long blocks LB#2 and LB#12 and two
short blocks SB#1 and SB#2. Compared with the embodiment of FIG. 26, pilots are loaded
on the long blocks LB#2 and LB#12 respectively positioned at one long block inside
from both ends of 1 ms TTI. Pilots of the long blocks LB#2 and LB#12 can be used as
a DM pilot, and since pilots of the short blocks SB#1 and SB#2 are allocated within
a scheduling bandwidth containing the frequency band of a specific user equipment
or for the entire bands, they can be used both as a CQ pilot and as a DM pilot.
[0093] FIG. 28 is an exemplary view showing pilot allocation according to still another
embodiment of the present invention.
[0094] Referring to FIG. 28, pilots are loaded on two long blocks LB#3 and LB#11 and two
short blocks SB#1 and SB#2. Pilots of the long blocks LB#3 and LB#11 can be used as
a DM pilot, and since pilots of the short blocks SB#1 and SB#2 are allocated within
a scheduling bandwidth containing the frequency band of a specific user equipment
or for the entire bands, they can be used both as a CQ pilot and as a DM pilot.
[0095] The steps of a method described in connection with the embodiments disclosed herein
may be implemented by hardware, software or a combination thereof. The hardware may
be implemented by an application specific integrated circuit (ASIC) that is designed
to perform the above function, a digital signal processing (DSP), a programmable logic
device (PLD), a field programmable gate array (FPGA), a processor, a controller, a
microprocessor, the other electronic unit, or a combination thereof. A module for
performing the above function may implement the software. The software may be stored
in a memory unit and executed by a processor. The memory unit or the processor may
employ a variety of means that is well known to those skilled in the art.
[0096] As the present invention may be embodied in several forms without departing from
the essential characteristics thereof, it should also be understood that the above-described
embodiments are not limited by any of the details of the foregoing description, unless
otherwise specified, but rather should be construed broadly within its scope as defined
in the appended claims. Therefore, all changes and modifications that fall within
the metes and bounds of the claims are intended to be embraced by the appended claims.
1. Verfahren, bei dem Subframes Pilotsignale zugeteilt werden, wobei die Subframes eine
Mehrzahl von Blöcken im Zeitbereich umfassen, wobei das Verfahren umfasst:
Übertragen, an einem Benutzergerät, eines Datendemodulation-, DM-, Pilotsignals, das
für die Demodulation von Daten verwendet wird, wobei das DM-Pilotsignal zwei Blöcken
zugeteilt wird, die so beabstandet sind, dass sie nicht aneinander angrenzen, wobei
ein erster Block der beiden Blöcke und ein zweiter Block der beiden Blöcke auf unterschiedlichen
Frequenzbändern übertragen werden; und
Übertragen, an dem Benutzergerät, eines Kanalqualität-, CQ-, Pilotsignals, das für
die Messung der Kanalqualität verwendet wird, wobei das CQ-Pilotsignal mindestens
einem Block zugeteilt wird, wobei das Frequenzband für das CQ-Pilotsignal breiter
als das für das DM-Pilotsignal ist und wobei sich die beiden Blöcke, denen das DM-Pilotsignal
zugeteilt wird, von dem mindestens einen Block unterscheiden, dem das CQ-Pilotsignal
zugeteilt wird.
2. Verfahren nach Anspruch 1, wobei der Subframe für die Uplink-Übertragung verwendet
wird.
3. Verfahren nach Anspruch 1, wobei die Blöcke, denen das DM-Pilotsignal zugeteilt wird,
und der mindestens eine Block, dem das CQ-Pilotsignal zugeteilt wird, nicht aneinander
angrenzen.
4. Verfahren nach Anspruch 1, wobei ein Intervall, in dem CQ-Pilotsignale zugeteilt werden,
gleich einem oder länger als ein Intervall ist, in dem die DM-Pilotsignale zugeteilt
werden.
5. Verfahren nach Anspruch 1, wobei der erste Block der beiden Blöcke in einen ersten
Subframe eingeschlossen wird, der eine Länge von 0,5 ms aufweist, und der zweite Block
der beiden Blöcke in einen zweiten Subframe eingeschlossen wird, der eine Länge von
0,5 ms aufweist und auf den ersten Subframe folgt.
6. Verfahren nach Anspruch 5, wobei das CQ-Pilotsignal in einem letzten Symbol des zweiten
Blocks übertragen wird.
7. Benutzergerät, das Subframes Pilotsignale zuteilt, wobei die Subframes eine Mehrzahl
von Blöcken im Zeitbereich umfassen, wobei das Benutzergerät umfasst:
einen Prozessor, der so konfiguriert ist, dass er:
ein Datendemodulation-, DM-, Pilotsignal, das für die Demodulation von Daten verwendet
wird, überträgt, wobei das DM-Pilotsignal zwei Blöcken zugeteilt ist, die so beabstandet
sind, dass sie nicht aneinander angrenzen, wobei ein erster Block der beiden Blöcke
und ein zweiter Block der beiden Blöcke auf unterschiedlichen Frequenzbändern übertragen
werden; und
ein Kanalqualität-, CQ-, Pilotsignal, das für die Messung der Kanalqualität verwendet
wird, überträgt, wobei das CQ-Pilotsignal mindestens einem Block zugeteilt ist, wobei
das Frequenzband für das CQ-Pilotsignal breiter als das für das DM-Pilotsignal ist
und wobei sich die beiden Blöcke, denen das DM-Pilotsignal zugeteilt ist, von dem
mindestens einen Block unterscheiden, dem das CQ-Pilotsignal zugeteilt ist.